Editing Data-flow diagram (section)

== DFD hierarchy ==
To make the DFD more transparent (i.e. not too many processes), multi-level DFDs can be created. DFDs that are at a higher level are less detailed (aggregate more detailed DFD at lower levels). The contextual DFD is the highest in the hierarchy (see DFD Creation Rules). The so-called zero level is followed by DFD 0, starting with process numbering (e.g. process 1, process 2). In the next, the so-called first level—DFD 1—the numbering continues For example, process 1 is divided into the first three levels of the DFD, which are numbered 1.1, 1.2, and 1.3. Similarly, processes in the second level (DFD 2) are numbered 2.1.1, 2.1.2, 2.1.3, and 2.1.4. The number of levels depends on the size of the model system. DFD 0 processes may not have the same number of decomposition levels. DFD 0 contains the most important (aggregated) system functions. The lowest level should include processes that make it possible to create a process specification for roughly one A4 page. If the mini-specification should be longer, it is appropriate to create an additional level for the process where it will be decomposed into multiple processes. For a clear overview of the entire DFD hierarchy, a vertical (cross-sectional) diagram can be created. The warehouse is displayed at the highest level where it is first used and at every lower level as well.<ref name=":1" />